This invention relates to line communications and more particularly to a line driver capable of producing output drive signals with amplitudes greater than the supply voltage.
Conventional line drivers commonly produce output signals with amplitudes that are limited by supply voltages. As integrated circuitry and process technologies improved, supply voltages reduced with associated reductions in the amplitudes of output drive signals.
Certain known schemes for increasing the amplitudes of output drive signals employ current-drive circuitry and transformer windings to produce output signals of greater amplitude than the supply voltages. However, such current-drive circuits commonly consume more power than voltage-drive circuitry and the inductive impedance inhibits rapid turn on/turn off operation.
In accordance with an illustrated embodiment of the present invention, a center-tapped transformer and associated drive circuitry deliver output drive signals with greater amplitude than the supply voltages, and with the associated drive circuitry greatly simplified to reduce power consumption and the processing involved for integrating the drive circuitry. P-MOS circuitry connected to a high-side supply voltage is eliminated in favor of transformer coupling from an N-MOS low-side supply voltage. The transformer also isolates the output drive signal from ground for enhanced versatility in connecting to communication lines. Output wave shapes for universal driver applications may be controlled in response to activation of a plurality of variable conduction elements in accordance with a selected logical sequence.